This invention relates to a data storage medium of the type described and claimed in U.S. Pat. No. 4,616,237. This patent (and the corresponding published European application No. EP-0107379A) discloses a data storage medium having a surface or a surface region which is strongly absorbant of at least a predetermined band of wavelengths of electromagnetic radiation, whereby the surface or surface region can be written-upon by such radiation, the surface or surface region including a layer of heat sensitive material which has a textured surface pattern which is a regular pattern comprising an arrangement of grooves or protuberances, the pitch of which is smaller than the shortest wavelength within said predetermined band of wavelengths, and the depth (peak-to-trough) of which pattern is at least 100 nm, the textured surface pattern being free from undercutting so as to be suitable for production or replication by moulding, casting, embossing or similar process against a tool, and the textured surface pattern being overcoated with a thin film of a material which has a high opactiy at the predetermined band of wavelengths. Information is stored on said data storage medium by irradiating selected areas on the surface of said medium to heat underlying heat sensitive material and change the local reflectivity of the surface of the medium. The depth of the surface texture may be less than 100 nm, e.g. 25 nm. Once written upon, such data storage media can be read using a read beam which, in many instances, will be in the form of a low power laser beam.